Marriage is under threat, we hear from some church leaders. Not by heterosexuals with an ever-increasing divorce rate, but by gay and lesbian people who want to express their religious faith in their civil partnership ceremonies.

Some leaders in my own church, the Church of England, as well as the Roman Catholic church have described this as an assault on religious liberty – and no doubt there is an aggressive secularist agenda to embarrass the churches, though aggressive secularists should note that we are pretty good at doing that ourselves without their help. Indeed, the religious liberty defence has a patronising and hollow ring to it when Quakers and Reform Jews are asking precisely for the liberty to register and bless civil partnerships in their own places of worship. They do not need Anglican or Roman Catholic bishops to "save them from themselves" – especially since both our churches have a shameful history of persecuting these very same faith groups.

So why does the liberty to introduce God into civil partnership ceremonies devalue marriage? It would appear that there just isn't enough of God to go around. One cannot, apparently, honour and bless one pattern of living a faithful and committed life, without somehow devaluing another. It is the theological equivalent of printing too much money.

Western Christianity has been here before. Prior to the Reformation, marriage was the option for the spiritual "also rans": serious Christians showed just how serious they were by committing to various forms of monasticism, or the "religious life" (the term itself is very revealing). Aspects of the ceremonies of profession to the religious life had, and have, parallels with the marriage service; for example, women religious wear a ring to show they are married to Christ. This is why Martin Luther came so to despise it – with all the zeal of an ex-monk married to an ex-nun who discovered sex and marriage in middle age. The "lifestyle" of these religious, according to Luther, undermined marriage by providing another form of commitment which "devalued" it.

"Married couples used to think that their being tied to each other was more a custom than an ordinance of God," claimed Luther in his Table Talk – that is until he had sent packing marriage's great rival, the religious life. When the religious life in the Church of England, pulverised at the Reformation, came back into its corporate life in the middle of the 19th century, many Victorian Anglicans saw it precisely in the same way: as a rival to marriage because it offered another sanctified, or blessed, way of Christian living. It introduced an element of "competition" into a spiritual monopoly.

The revival of the religious life in Anglicanism, and the honoured place it now has, goes to show how we can as a church change our mind and rectify our mistakes. It also goes to show that there really is enough of God to go around; that different ways of faithful living do not compete with each other but add to the enrichment of the whole. Gay and lesbian people of faith actually want God's blessing at an important time of public commitment. So much for aggressive secularism.

Stability, love, faithfulness, commitment: these are the things in human relating that matter and the things the Church of England should be doing its best not to disparage or demonise but to foster and celebrate – in short, to bless. There really is enough of God to go around.